Heat recovery from the flue gas is a well known technique using so-called air heaters that transfer heat from the flue gas leaving the boiler to the primary air that is necessary to burn the fuel, for example coal, in the boiler.
Further on from U.S. Pat. No. 5,293,841 a heat shifting unit is known that shifts additional heat from the flue gas to the primary air using two heat exchangers, one of them being connected to the flue gas line and the other being connected in the primary air line. The heat is transferred between these two heat exchangers by means of a heat carrying medium that flows through both heat exchangers in a closed loop.
Both the air pre-heater and the above described heat shifting unit transfer heat from the flue gas to the primary air.
From U.S. Pat. No. 5,293,841 a first heat exchanger is known, transferring heat from the flue gas to the feed-water of the power plant. This first heat exchanger is integrated in a bypass of the air heater and an additional second heat exchanger for feed-water heating in series with the condenser and low pressure (LP) feed-water heaters. This arrangement does not allow efficient flexible operation in terms of variable heat transfer due to load and unit operation time changes as well as temperature changes. Further on, this arrangement requires a lot of space, making the arrangement not applicable as a retrofit solution in existing power stations.
Consequently, it is the object of the claimed invention to allow the heat transfer between the flue gas and the feed-water with little extra space needed in the flue gas line of the power plant resulting in a better applicability and the possibility to install a heat exchanger between the flue gas and the feed-water in existing power plants resulting in an improved overall efficiency and dust precipitation of the flue gas.
This object is solved by a power plant comprising a boiler, a flue gas line, a precipitator system and a first heat exchanger, whereby the heat exchanger is installed upstream of the precipitator system in the flue gas line by installing the heat exchanger adjacent to the precipitator system having either horizontal or vertical gas flow.
The claimed invention allows a flexible as well as an efficient operation of the power plant at different load points.
An advantageous embodiment of the claimed invention is characterized in, that upstream of the first heat exchanger a diffuser is installed, and that the heat exchanger and a precipitator system use that same diffuser and the gas flow is horizontal. This saves costs and reduces the space required for installing the first heat exchanger. Typically there will be more than one heat exchanger in parallel. The number of heat exchangers in parallel depends on the number of precipitator passes in parallel.